X-ray tube comprising a disk-shaped rotary anode



Nov. 22, 1949 B. COMBEE 2,489,080

X-RAY TUBE COMPRISING A DISK-SHAPED ROTARY. ANODE Filed July 18, 1947 I wwzwroxe .aw/Pr GOA/55E WWW ' ATTORNEY Patented Nov. 22, 1949 ROTARY ANODE Bart Combe, Eindhoven, ;Netherlands, assignor to Hartford National Bankland Trust Com pany, Hartford, Conn, trustee Application: July 18, 1947-; Serial' No. .7 61,965

In the Netherlands July: 17", '1946 Section 1, PubIicLa-w 690Q-Augi1st 8, 1946' Patent 'expircs July 17,1966

. 2 Claims. (Cl; 250a-148') In screening by means of X-rays the time of the anode but substantially not influence the heat examination must not be limited by the loading emitting capacity.' capacity of the X-ray tube as is the case inmak- However, this known construction permits of ing exposures, when the X-ray tube is damaged increasing'the loading 'capacity of an 'X-ray tube upon exceeding the permissible loading time. In..:5 fhaving-a disc-=Shaped' anode which is-adapted to order to satisfy this condition it is required for be operated'continuousl'y. This "fact isfu'tilised the X-ray tube to remain-operative practically by'the inventionwhich concerns anX-I'ayftube continuously. For a short time afterstarting up having-a disc-shaped anode with whichthe imthe tube, the heat evolved by electrons imping- 'pa'ct=disc for the electrons is provided; ona disc ing on the anode is mainly absorbed by the anode' m 'consisting' of 'nickelor' other metal, the melting As the temperature of the anode increases, an point of which is at least as'high'and' whi'ch is ever increasing quantity of heat is carried off better workable than tungsten. According [to until the average quantity of heat evolved per 'the invention the'-=carrier-disc"is providedwith unit time and the heat carried 01f per unit'time a rim having s uch'a large'heat radiating surface are ultimately equal. In using a tube having a.i- :"that at the maximum 'permissibletemperature rotary anode from which the heat evolved thereat least one third of the heat produced in the in is carried off by -radiation,-:theload is deteranode is carried off.

mined by e temperature of he anode, which Withrotary anodes it is known to provide the must not exceed the maximum permissiblevalue, impact-disc for the electrons on a copper meniand by the size of the radiating surface Enlargf ='go b The low melting temperature of this metal ing the Surface of a disc-shaped anode, -in order e t' t t an'impdiment to s use as a thermal to increase the load, entails the disadvantage-that itt r, Along this path heatis carried off'even the diificulties experienced inthe-manufacture of during operation, it i r e u the thermal anode-discs increaseas the diameter OhthefllSC emission is smauzrelatively t0 the Supply of heat. is larger- In this event moreover, h .i so that the member acts as a heat container, the strains of a rapidly rotating disc increaseto such operation having to be interrupted as soonasflthe a degree that there is a risk of the production of maximum fpermissableitemperature gismreachd. cracks 1n the -mater1al.- Finally, a large d1- In using metals having a higher meltinghpomt ameter of the m hg 5129 p 1 vthe thermal radiation obtained at a high-temtube y to h the apparatus lk peratureincreases the dissipation' of heat' lso P hlgher Welght! i -my tube arranged that a'heat container canbe-dispensed with-and m an envelope fined Wlth h th d the-tube can be'operated fora longertime.

tubes are known m W m e anO-e- In order that the invention may be clearly dlsc 1S m thermal relafilon through a Shaft Wlth understood and readily carried into effect it will i g fi gf g fig fi g af fig g fi now be explained more fully with reference to 1g ea cap 1 o duced in the anode is carried off and radiated E zfi fi i e m Whlch X'raY by the cooling member at a comparatively low 1 ere 15 represented 111 P temperature. This cooling member is located in fi ifi lcal. th f the tube where it surrounds the supporting mem- 40 note g 1b 8 re g 1 1 bers for the construction causing the anode to 5 e g ass 11 Surrouh he Ca de 2 rotate so that great care has to be taken that and the anode The hlllb and the Cathode a the temperature of the said member remains berepresehted dlagramlhatlcally and ay be of low the temperature detrimental to the life of the conventlohal cohstlllchonsaid construction. It has been found that by this The anode compllses O p r s e connected condition the heat transference from the anode by the Shaft one P recelvlhg the beam o to the cooling member is limited to at most 15% electrons emitted by the cathode, and the other of the heat produced in the anode when the size P ri in a r ary construction. The

of the rotor is to be kept within reasonable limits. anode is supporte y ll be ings 5 which are I the form of c t ti of a X-ray secured to the stationary shaft 6 and connected tube having a disc-shaped rotary anode the imto the rotor. The latter consists of a copper pact-disc for the electrons is provided on a disc jacket 1 provided with a lining 8 which consists consisting of refractory metal which is better of iron for the electromagnetic driving. The workable than tungsten. This measure has for jacket carries the shaft 4 and the tungsten its purpose to increase the thermal capacity of anode-disc 9 which is provided on a disc I0 consisting of metal which is better workable than tungsten, this disc having a rim ll.

Through the contact surface between the anode-disc 9 and the carrier plate 10 a quantity of heat passes to the latter. The temperature to which the plate 10 can be heated depends upon the metal from which it is made. This tempera-- ture should not be exceeded during operation.

Suppose that the disc-anode has a workin temperature of 1500 K.; the specific thermal radiation then being 6.5 watt/sq. cm. for tungsten."

The temperature of the carrier plate may, for instance, be 1200 K.; this plate may consist of molybdenum or even of iron, the specific radiation for a well blackened surface then likewise being 6 watt/sq. cm. When the tube is to be loaded with 500 watt, half of which is radiated by the anode, whereas the other half is carried oil to the carrier plate and, by the shaft, to the rotor, the disc-anode requires a surface of 250 Kg =40 sq. cm.

the diameter consequently being 50 mms.

In order that the ball bearings should not be affected by the heat, the temperature of the rotor must not exceed 600 K. the radiation coeflicient of a blackened copper surface of 100 sq. cm. is approximately 2.95 X 10- The thermal emission is proportional to the radiation coefilcient and the fourth power of the temperature, whence it follows that the emitted quantity of heat E=S2.T is equal to 39 watts. Consequently, the carrier member has still to radiate 211 watts which means that the radiating surface must approximately be -30 sq. cm.

' In the event of a diameter of 4 cms. the rim has a height of 24 mms.

In the absence of the carrier member the anode-disc, in order to be able to withstand load, must have a surface of and a diameter of 67 mms.

In a very advantageous construction the carrier-disc consists of titanium iron which isprovided with a black surface obtained by oxidation. The relation between the black layer and the metal surface is not appreciably affected when the carrier-disc is heated to incandescence, so that, in

the same -71 sq. cm.

4 contradistinction to other metal surfaces blackened in the same manner, a permanent improvement of the radiation coemcient is obtained.

When making use of the invention an X-ray 'tube employed for screening and having a discshaped rotary anode can be loaded with impunity to a degree 50% higher than it was possible in the past. When providing the rim with apertures for reducing the weight of the carrier-disc and its moment of inertia this improvement is not appreciably afiected.

What I claim is:

1. An X-ray tube having a rotating anode comprisingan anode disc of tungsten, and a supporting disc of titanium iron provided with a black oxidized surface, said supporting disc being provided with a rim portion having a surface area for radiating at least one-third of the heat produced in said anode disc when said anode disc is operated at the maximum operating temperature.

. 2. An X-ray tube having a rotating anode comprising an anode disc of tungsten, and a heatradiating cup-shaped supporting member for the anode disc of black oxidized titanium-iron provided with a plurality of apertures in the rim portion thereof, the rim portion having a surface area for which at least one-third of the heat produced in the anode disc at the maximum operating temperature thereof is radiated from the supporting member.

BART COMBEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

